The present invention relates to a system and method for visualizing a needle within biological tissue. More particularly, the invention relates to a system and method for visualizing a needle and locating anatomical structures within a body by utilizing equipment sensitive to the unique absorption and scattering characteristics of the target structures.
Every day many hundreds-of-thousands of medical procedures involving the puncturing of blood vessels are performed. Venipuncture, as it is known, is required in order to administer emergency fluids, blood components, and anesthetics during operations, or to allow the drawing of blood for biochemical analysis. Venipuncture, which is often the rate-limiting step when administering intravenous compounds, can take as long as a half hour, or longer when the patient is a neonate, infant, geriatric, obese, or burn patient. Notwithstanding the enormous financial burden on our society as a whole because operating rooms and health-care providers must wait as an intravenous line is placed, the delay in placing an intravenous line can in fact be life threatening. Furthermore, there are additional problems associated with multiple venipunctures caused by the clinician's failure to locate the vessel.
The reason venipuncture is sometimes difficult to do is that the blood vessels are often located relatively deep within the tissue which, because of its absorptive and scattering optical properties, makes visualization of the blood vessel impossible under normal conditions. Furthermore, the situation is made worse by the fact that the vessel may spasm and constrict if it is manipulated too much. Consequently, health care providers have a need to visualize blood vessels in real-time during venipuncture in order to reduce the risk to the patient, save time and reduce the cost of the procedure. Furthermore, reducing the time of the procedure limits the providers' exposure to a potentially contaminated needle. Finally, visualization of vascular tissue can provide important diagnostic and therapeutic information about certain diseases such as thromboses, cancers or vascular malformations.
In the mid-1970's an instrument was devised that purportedly provided surgeons with the ability of visualizing superficial blood vessels. It consisted of a visible light source which, when pressed up against the skin, transilluminated the subcutaneous tissue and aided in the visualization of superficial blood vessels. The blood-vessel transilluminator made use of the different absorption properties of blood and tissue. Because blood strongly absorbs certain wavelengths of light, while fat and skin absorb other wavelengths, a health-care provider purportedly could visually distinguish the position of the subcutaneous blood vessel with the naked eye. The transilluminator has essentially fallen into disuse because it fails to provide enough contrast between the blood vessel and tissue to be of use other than for venipuncture of superficial vessels. Furthermore, some versions of the blood-vessel transilluminator caused thermal damage to the patient.
In response to the transilluminator's failures, several references proposed using an illumination wavelength which penetrates surface tissue to a depth of the deep vessels but which is also highly absorbed by the blood. See, e.g., Cheong, W-F, et al., “A Review of the Optical Properties of Biological Tissues,” IEEE Journ. Quant. Elec., 26:2166-2185 (1990). These references, however, did not disclose efficient means of effectively illuminating and detecting the body structures of a vessel.
Later devices produced more effective results by employing a polarizer to detect back-scattered illumination reflected from a body. See e.g. U.S. Pat. No. 6,032,070, entitled Method and Apparatus for Detecting Electro-magnetic Reflection from Biological Tissue, which is herein incorporated by reference. Using reflected electromagnetic radiation singularly scattered from target tissue, these methods enabled medical personnel to effectively view anatomical structures such as blood vessels in high contrast with its surrounding tissue. Accordingly, present procedures enable medical clinicians to visualize internal anatomical structures such as blood vessels.